How Z-Wave Controllers & Devices Work

HOW DO Z-WAVE CONTROLLERS AND DEVICES WORK?

Z-Wave works very efficiently as a wireless communication. The nodes communicate messages to each other, to carry out its list of instructions during a typical day in the home. This includes managing your energy system, and/or even your home security system. Entirely, it is up to you when your lighting system comes on, or when the blinds close, or whether you want to set your house alarm simultaneously with the central locking.

Z-Wave technology is very versatile, meaning you can make your home wireless system as small or large as you need. There are many types of Z-Wave Devices which have different functions which allow you to categorise them, and manage them effectively whilst saving yourself money.

The Z-Wave system has three layers: radio, network and at the top an application layer.

These three layers work together so that communication between the devices can succeed. It also means that numerous communications can occur between different nodes and devices simultaneously.

The Application Layer of the Z-Wave product defines and specifies what and why two nodes can communicate with each other.

In the Z-Wave terminology controlling devices are called controllers, reporting devices are called sensors and controlled devices are called actuators. It is also possible to combine a logical sensor controller or actor function within one physical device.

Actors switch either digital (on / off for a electrical switch) or analogue signals (0 % …. 100 % for a dimmer or venetian blind control).

Sensors deliver either a digital signal (door, glass breaking, motion detector, window button on the wall) or an analogue signal (temperature, humidity, power).

In today’s market of Z-Wave devices, there is a surprisingly short list of different product categories. Nearly all Z-Wave devices on the market can be categorised into one of the following function groups:

Electrical switches are designed either as plug in modules for wall outlets or as replacement for traditional wall switches (digital actors). It’s also possible to have these actors already built into certain electrical appliances such as electrical stoves or heaters;

Electrical dimmers, either as plug in modules for wall outlets or as replacement for traditional wall switches (analogue actors);

Motor control, usually to open or close a door, a window, a window sun blind or a venetian blind (analogue or digital actors);

Electrical Display or other kind of signal emission such as siren, Led panel, etc (digital actors);

Sensors of different kind to measure parameters like temperature, humidity, gas concentration (e.g. carbon dioxide or carbon monoxide) (analogue or digital sensors);

Thermostat controls: either as a one knob control or using a temperature display (analogue sensors);

Thermostats controls such as TRVs (Thermostat Radiator Valves) or floor heating controls (analogue or digital actors);

Remote Controls either as universal remote control with IR support or as dedicated Z-Wave Remote Control with special keys for network functions, group and/or scene control;

USB sticks and IP gateways to allow PC software to access Z-Wave networks. Using IP communication these interfaces also allow remote access over the internet.

Command Classes

All communication within the Z-Wave network is organised in Command Classes. Command Classes are a group or commands and responses related to a certain function of a device.

A normal on/off switch is referred to as a binary switch. The basic function of a binary switch is to be switched on and off. With a Z-Wave system it is also possible to know the status of the switch, hence a status request function and a status report function is required too.

The Command Class for a binary switch consists of three different function responses, commands or reports.

Binary Switch – Set: is sent from a controller to the switch to turn the switch on or off

Binary Switch - Get: Is sent from the controller to the switch to request a report about the switching state.

Binary Switch – Report: is sent from the switch back to the controller as a response to the Binary Switch Get Command.

These three commands and responses are grouped and referred to as command class ‘Binary Switch’. If a certain Z-Wave device supports the command class binary switch it is supposed to be able to deal with all these commands:

The switch needs to understand the set command and set the switch accordingly;

The switch is able to receive a get command and is able to response with a report command in the proper format.

The Command Class - Basic

Command Classes represent the functions of a certain Z-Wave device. Switches will support different command classes rather than thermostats.

To make sure Z-Wave devices can communicate with each other even without further knowledge about their specific function, there is one special command class called “basic”.

The basic command class consists of two commands and one response:

- SET: set a value between 0 and 255 (0x00 …0xff);

- GET: ask the device to report a value;

- REPORT: response to the Get command. Reports a value between 0 and 255 (0x00 … 0xff);

The specialty of the basic command class is that every device will interpret the basic commands dependent of its specific functionality.

A binary switch will switch on when receiving a value 255 and switch off when receiving a value of 0;

A thermostat may turn into a convenience temperature mode when receiving value = 0 and may turn into a energy saving mode when receiving a higher value;

A temperature sensor will issue a basic report and send a integer temperature value;

A door sensor will either send out a value = 0 in case the door is closed or a 0xff when the door is opened.

The basic command class is the smallest common denominator of all Z-Wave devices. Every Z-Wave device must support the Basic command class.

Device Classes

To allow inter-operability between different Z-Wave devices from different manufacturers, certain Z-Wave device must have certain well-defined functions above and beyond the basic command class.

The structure behind these requirements is called device class. A device class refers to a typical device and defines which command classes are mandatory to support.

Device classes are organised as a hierarchy with three layers:

Every device must belong to a basic device class;

Devices can be further specified by assigning them to a generic device class;

Further functionality can be defined as assigning the device to a specific device class.

Basic Device Class

The BASIC device class makes a distinction merely whether the device is a controller, a Slave or a Routing-Slave. Therefore every device belongs to one basic device class.

Generic Device Class

The generic device class defines the basic function as device is supposed to offer as a controller or slave. Current generic device classes are:

General controller (GENERIC_CONTROLLER)
Static controller (STATIC_CONTROLLER)
Binary switch (BINARY_SWITCH)
Multi level switch (MULTI_LEVEL_SWITCH)
Binary sensor (BINARY_SENSOR)
Multilevel-Sensor (MULTILEVEL_SENSOR)
Meter (METER)
Input controller (ENTRY_CONTROL)
Thermostat (THERMOSTAT)
Window Venetian blind controller (WINDOW_COVERING)

Specific Device Class

Assigning a specific device class to a Z-Wave device allows it to specify the functionality of the device further. Each generic device class refers to a number of specific device classes. Assigning a specific device class is voluntary and only makes sense, if the device really supports all specific functions of a specific device class.

Special device classes are, for example:

Setback Thermostat (SETBACK_THERMOSTAT) is a specific device class of the generic device class “Thermostat“;

Multi-level Power Switch (MULTILEVEL_POWER_SWITCH) is a specific device class of the generic device class Multilevel Switch;

In case the Z-Wave device is assigned to a specific device class, it is required to support a set of command classes as functions of this specific device class.

These required command classes are called mandatory command classes and they are individual of certain generic and specific device classes.

Above and beyond the mandatory device classes, Z-Wave devices can support further optional command classes. They may be very useful but the standard does not enforce the implementation of these classes.

A Z-Wave manufacturer is allowed to implement an unlimited number of optional device classes, however if these device classes are implemented, the standard defines how these commands and functions are to be supported.

The basic device class, the generic and, if available, the specific device class is announced by the device during inclusion, using a Node Information Frame.

As well as the device classes, the Node information frame also announces all optional command classes of the device included. With this announcement, a controller can control and use an included Z-Wave device according to its functionality.

A Z-Wave device works according to the Z-Wave standard if:

It belongs to a basic device class and a generic device class, and is able to report these classes on request using a Node Information Frame.

It supports all mandatory command classes of the basic and generic command class by sending commands and reports as well as accepting and executing commands according specification of the command class;

In case a specific device class is defined the mandatory command classes of this specific device class, needs to be supported as well and the specific device class needs to be reported on request;

In case optional command classes are implemented, these command classes need to be announced in the Node Information Frame on request and need to be supported according to the Z-Wave command class specifications.

Z-Wave defines a broad variety of command classes covering almost every aspect of home automation and control. Nevertheless it’s possible that manufacturers want to implement further functionality not already defined in a command class specification.

The command class “proprietary function” is defined to cover these needs. A proprietary function would allow a manufacturer to implement specific functions which can then be used only by other devices supporting this proprietary function as well.

The use of a proprietary function is subject to approval by the Z-Wave alliance certification authority and is required to be documented extensively. So far only very few device make use of this function. Typically new requirement result sooner or later in an amendment to the existing standard, which makes this function part of the official standard and any proprietary extension becomes obsolete.

Selection of Devices - Controllers

The selection of devices is always based on the desired function of the network. A network always consists either of a central remote control or a central static (fixed location) gateway on a dedicated device (e.g. IP gateway or set top box) or as software on a PC.

Controlling a Z-Wave network only from a remote control is only recommended if:

There are only few devices to be controlled (less than ten is a good measure);

No battery operated devices are in the network;

No time dependent functions like shutting down the window blinds at a certain time of the day are required.

Otherwise it’s highly recommended to use a static controller as IP gateway or PC software. To use PC software an additional USB adapter, typically a USB stick, is needed.

Selection of Devices - Slaves

Portable dimmers and switch, also called “smart plugs” or “wall outlet plugs” are easy to choose. It’s only recommended to check the maximum switching capability (in W or A). Design issues may play a role as well.

For wall switches the design or the plates play an important role. Switches shall have the same industry design as wall outlets and other wall installations such as antenna and phone jacks or Ethernet outlets.

Its possible to turn existing legacy switches into Z-Wave switches by using special insert, which are placed behind the legacy switch. However the depth of the pattress box needs to support this.

Z-Wave – The future of Energy Saving in the Home

With so many compatible devices and so many ways of programming and personalising these devices and controllers to work together, many options are available. With this system you can go away on holiday without those second thoughts, ‘did I leave the bathroom light on?’ or ‘did I turn down the thermostat?’ With VERA technology, you can pre-programme all of these instructions, with little effort.

The controller, VERA for example, can control lamp modules, thermostats, in-wall light switches, power strips, alarm sensors, garage door openers, window blinds, and home theatre solutions.

With its timeless components, this system won’t need replacing in six months time. You can add and develop it, in whatever way you like. Components will always be compatible.

You can customise your electrical system to what you need. For example, you can save energy by making sure all the lights are off, and the thermostat is turned down when you go to work – VERA can take care of this.

Whilst on holiday, you may hear there has been a cold snap in your home country – via the VERA Gateway, you can enter your home network, and turn the thermostat up from the comfort of your hotel room.